A method for manufacturing a tire is proposed in which a green tire is shaped by stamping each of tire-constitutional members on the outside of a toroidal-shape carcass member fixed onto a rigid core or a shaping drum and vulcanizing it in order to make the shape of a product tire or dimensions of each of the members highly accurate. In this manufacturing method, a rubber member among these tire-constitutional members is stamped by winding a continuous rubber ribbon in plural turns, and according to this manufacturing method, when compared with the case where a rubber having a cross section corresponding to a cross section of a member in the product tire is wound only once for formation, there is no need to extrude a rubber member with a large cross-section which can reduce the size of an extruder and moreover, by directly winding a rubber ribbon extruded from a smaller-sized extruder onto a toroidal-shape carcass member, the need of a large amount of an intermediate stock of members which has been necessary for production of other types of tires can be eliminated.
Also, when shaping green tires in different sizes, members with different cross sections can be formed with a rubber ribbon in the same cross sectional shape only by changing the number of times or position of winding and it has a feature that green tires in difference sizes can be formed continuously.
Moreover, the tire made of the rubber member formed by winding the rubber ribbon in plural turns in this way becomes high quality in the uniformity and tire balance, since there is no joint across the total width of each member.
However, it has been found out that the following problem may occur if this manufacturing method is applied to a tire having characters or lines different in color from the surroundings on the side wall part.
FIG. 1 is a perspective view showing a portion of a side wall part of a product tire on which the character “I” is formed in white, for example. FIG. 2 is a sectional view corresponding to II-II arrow view in FIG. 1 showing the state in the middle of manufacture of the tire portion where this character is formed, and FIGS. 3(a) and 3(b) are a sectional view and a perspective view showing the detail of this character portion in the product tire. In FIG. 1, B indicates a black rubber portion and W for a white rubber portion, and in FIGS. 1 to 3(a) and 3(b), T is an arrow showing the circumferential direction of the tire. The a-a arrow view in FIG. 3(b) corresponds with the cross section of FIG. 3(a).
In order to form this white character, as shown in FIG. 2(a), at the stage to shape a green tire, after a black side wall rubber 92 is stamped on the outside of a carcass member 91 to be a base, a black cover rubber 93 is stamped on a side wall part on which the white character is to be expressed. And in vulcanizing this green tire, as shown in FIG. 2(b), the white character portion is projected from the other portions using a mold with a recess portion corresponding to the white character.
Then, as shown in FIG. 3(a), the projected portion is buffed to remove the cover rubber 93, and the white side wall rubber 92 appears from under it and the white character can be formed. However, if the cover rubber 93 is formed by overlapping a narrow-width ribbon, as shown in FIG. 3(b), a step between the ribbons appears on a cross section 93a in which the over-lapping portion between the ribbons is buffed, which causes a problem on appearance. Even if the ribbon is wound so that a gap between the ribbons becomes zero in order to solve the problem, it is actually difficult to bring this gap to zero, and a gap or overlapping will occur and the problem on appearance has not been solved yet.
The present invention has been made in view of the above problem and has an object to provide a tire having characters or lines in color different from the surroundings on a side wall part, a manufacturing method in which a large extruder is not needed, the other types of tires can be efficiently manufactured since size switching is easy, the shape and the dimensions of the members are highly accurate, the uniformity and the tire balance are excellent and a tire with sharp profiles of characters or lines and having no problem on appearance, a tire manufactured with the manufacturing method and a device used in this manufacturing method.